1. Field of the Invention
This invention relates to an improved process for the liquid phase oxidation of an organic substance-containing effluent in the presence of a copper catalyst for reducing the chemical oxygen demand (hereinafter referred to as COD) in the effluent and also to a process for the convenient recovery of the employed copper catalyst.
2. Description of the Prior Art
There have been proposed and are known a number of processes for treating effluents containing relatively high concentrations of organic substances. Typical of these processes is a liquid phase oxidation process such as disclosed in U.S. Pat. No. 2,665,249 issued to Frederick J. Zimmerman. If, however, a high rate of oxidation is desired, this liquid phase oxidation process dictates the use of suitable high temperatures in the range of from 232.degree. to 329.degree. C. This presents many problems such as of economy, safety in operation and corrosion of construction materials and apparatus for the plant, so that a process using relatively lower temperatures and relatively lower pressure conditions has been desired.
In recent years, there has been proposed as an improvement of said liquid phase oxidation treatment in order to achieve a higher treating rate, a process using a catalyst together with lower temperature and lower pressure conditions such as disclosed in Japanese patent publication No. 22275/1969 issued to T. Takahashi, in which process organic substances contained in effluent are wet oxidized at a temperature above 160.degree. C. in the presence of copper or a copper compound while continuously blowing a free oxygen-containing gas into the effluent. In this Japanese patent publication, however, there is no particular description regarding the pH range which is effective for the liquid phase oxidation treatment for the effluent.
Under these circumstances, the present inventors have made an intensive study of a process of treating organic substance-containing effluents by liquid phase oxidation under high temperature and high pressure conditions and have found that the liquid phase oxidation treatment should be conducted under neutral or alkaline conditions in consideration of the corrosion problem of the construction materials. However, it has also been found that, in some cases, the copper and/or copper compound catalyst used in the liquid phase catalytic oxidation process does not show any suitable catalytic activity under neutral or alkaline conditions. Further, it has been found that, in practicing the liquid phase catalytic oxidation process on an industrial scale, the copper and/or copper compound catalyst should preferably be removed and recovered from the effluent to such an extent that it will not interfere with a microorganism treatment of the effluent which is ordinarily conducted prior to discharge of the treated effluent from the liquid phase oxidation system. A practical process for the removal and recovery of the copper and/or copper compound catalyst from the treated effluent has not as yet been developed.